Transmission of signals by optical fibers over long distances meets problems of attenuation and chromatic dispersion. Thus, a signal that is very monochromatic at the beginning of the line will be dispersed and will no longer have sufficient level at the end of the line to be correctly reconstituted. The result is therefore a loss of information.
Early techniques used to resolve this problem were to install signal regeneration stations. The signal is first converted to an electronic signal, regenerated and retransmitted. This regeneration system was very expensive for a single transmission channel and thus for a single transmission wavelength.
Another known solution is optical amplification. The chromatic dispersion of the wavelength is compensated for by a fiber of opposing dispersion and attenuation is compensated for by an optical amplifier. That solution requires high-performance transmitters and receivers and remains expensive in single channel.
Moreover, to augment the number of signals to be transmitted on the line, multi-channel solutions rapidly became necessary. A plurality of transmitters uses different wavelengths. The data is then modulated to quasi-monochromatic signals and the quantity of information transmitted is thus augmented. The signals are then multiplexed before transmission on the optical line. Amplification and optical compensation are then realized simultaneously on the multiplex. That method has the disadvantage of using very expensive transmitters for each channel.
In the area of multiplexing in wavelength or WDM for Wavelength Division Multiplexing, there already exists a device and a process for regenerating data in an optical transmission in EP 1 233 567. The entering data stream is first demultiplexed by a demultiplexer in wavelength. Delays are then introduced in a specific manner for each channel, that is to say, the delayed signals are multiplexed again for each wavelength. The device comprises a modulator modulated by a high-frequency clock and a photodetector for an automatic optical adaptation of the delay lines.
That process is a method of signal regeneration successively using a demultiplexing, then a multiplexing of the signals. The delays introduced are of the optical type by virtue of the photodetector. It does not supply a solution for the shared transmission of different signals coming from a plurality of transmitters.